SYDNEY (Reuters) - An Australian lawfirm formally filed a class action suit against Commonwealth Bank of Australia on behalf of shareholders on Monday, accusing it of failing to disclose widespread breaches of anti-money-laundering rules. The lawsuit by law firm Maurice Blackburn against the nation's biggest lender follows one by the federal agency AUSTRAC, which has accused it of more than 53,000 breaches of anti-money laundry rules - breaches which have exposed it to billions in dollars of fines. The suit, which had been previously flagged by Maurice Blackburn and litigation financier IMF Bentham Ltd, said shareholders had suffered a significant share drop in the wake of AUSTRAC's accusations. The law firm's statement on Monday did not specify the level of damages sought. CBA has not disputed that it processed tens of thousands of illicit transfers but argues the breaches were largely caused by a software glitch and contests its level of responsibility. A CBA spokesman had no immediate comment on Monday. The bank's stock is down 8.5 percent since AUSTRAC announced its civil lawsuit against CBA in August. CBA shares were up 0.7 percent by mid-morning on Monday, in line with the broader market. (Reporting by Byron Kaye; Editing by Edwina Gibbs)